Soluble vs. Insoluble Fibre: What’s the Difference?
You may have heard that fibre is good for us and that we generally need more of it, but do you really know what it is?
Fibre is a carbohydrate but with an interesting twist. Unlike other carbohydrates such as sugars or starches, fibre does not get digested and absorbed in the traditional sense. Fibres are long chains of carbohydrates that withstand our body’s digestive process. In other words, they do not get broken up by our digestive enzymes nor do they provide us with any calories, or energy. It is their indigestible nature which provides us with unique health benefits.
What’s more, is that there are two distinct types of fibre, soluble and insoluble which differ in their physical structure and impact on health. When soluble fibre, found in oats, chia seeds, psyllium husks, legumes and some fruits, is combined with water it forms a gel-like substance. In the digestive tract, this viscous gel-like substance helps combat diarrhea and has been shown to improve blood sugar control by slowing down the release of glucose into the bloodstream. Along with its effect on blood sugars, soluble fibre also disrupts the absorption of dietary cholesterol and can improve LDL (or “bad”) cholesterol.
There is also evidence that suggests that soluble fibre plays a role in satiating hunger (or keeping us fuller for longer). This may explain why a bowl of oatmeal is so filling or “sticks to your ribs”, as they say. Some types of soluble fibres are also broken down and fermented by the beneficial bacteria in our large intestine as a food source, or prebiotic.
Unlike soluble fibre, the insoluble fibre found in many fruits, vegetables and whole grains does not form a gel in the digestive tract. Rather, it serves to provide bulk and structure to our stool which benefits our large intestine. Diets high in insoluble fibre are associated with less constipation, and helpful in the management of diverticular disease and hemorrhoids.
Current dietary recommendations for fibre are 25 grams per day for adult women and 38 grams per day for adult men. Most people eat well under this amount of fibre. While both types of fibre are needed, it’s not generally necessary to keep a daily tally of the amounts of each type of fibre you are eating. You’d probably drive yourself mad doing this. The good thing is that most sources of fibre do contain a bit of both types but differ in the proportions of each they contain. Some foods contain a higher percentage of soluble fibre while others contain more insoluble fibre. If you need better blood sugar or cholesterol control, you may benefit from choosing foods with a higher percentage of soluble fibre (like oats or pears), while those with constipation may want to include those with more insoluble fibre (like wheat bran).
For the most part, what’s really important is to focus on total fibre intake and ensure that it meets the recommended amount (25 g for women and 38 g for men). This can be done by including lots of fruits, vegetables, whole grains, nuts and seeds in your diet each day. When reading the nutrition facts label, look for foods with at least 2 grams of fibre per serving. Those with 4 or more grams of fibre are considered ‘high fibre’ and definitely worth including. If you want a complete list of fibre containing foods, check here.
An important note: remember to increase fibre intake slowly and to make sure you are drinking enough fluids. Fibres need fluids, or else you’ll find yourself constipated (or more constipated). While there isn’t a specific recommendation for the amount of fluids to be drinking per increment of dietary fibre, you can start with 6-8 cups of fluids per day (water, tea, coffee, soup, etc) and take more if needed (if exercising or in hot, humid weather).
Kate Chury
Registered Dietitian
Kate is a is a Registered Dietitian in Calgary, Alberta.
